Conventionally, in a pure electric vehicle (PEV), a so-called hybrid electric vehicle (HEV) provided with an engine and a motor, and the like, a nickel-metal hydride (Ni—MH) battery mainly is used as a main power source for driving a motor due to its high energy density (that is, the ability to accumulate energy in a compact manner) and a high output density. In such a PEV and an HEV, a plurality of cells are combined to form one combined battery so as to supply a sufficient output with respect to a motor, and the combined battery is mounted as a high-voltage battery.
Such an HEV or the like includes a high-voltage circuit for driving a motor using a high-voltage battery as a driving source, and a low-voltage circuit for driving electronic equipment such as acoustic equipment using a low-voltage battery as a driving source. Furthermore, the high-voltage circuit includes an inverter for driving a motor.
In a motor-driven vehicle such as an HEV, in order to ensure the safety for a human body, it is required that leakage from a high-voltage circuit side to a low-voltage circuit side be detected, and when leakage is detected, the power from a high-voltage battery is interrupted.
FIG. 5 is a functional block diagram showing a partial configuration of a conventional motor-driven vehicle. In FIG. 5, a motor-driven vehicle 100 includes a high-voltage circuit 10 for driving a high-voltage load 11 such as a motor, a low-voltage circuit 20 for driving a low-voltage load 21 such as various kinds of electronic equipment, and a leakage detection apparatus 300 for detecting the presence or absence of leakage between the high-voltage circuit 10 and the low-voltage circuit 20.
The high-voltage circuit 10 includes a high-voltage battery 12, a second switch portion 13 for conducting/interrupting power from the high-voltage battery 12 with respect to the high-voltage load 11 side, and an inverter 14 for driving the high-voltage load 11.
The high-voltage battery 12 is composed of a plurality of secondary batteries (e.g., Ni—NH secondary batteries) 121 connected in series, and is capable of outputting a high voltage (e.g., 400 V) required for rotating a motor as a driving source for allowing the motor-driven vehicle 100 to run. The second switch portion 13 is composed of a relay and the like, and has a predetermined minimum current capacity required for driving the high-voltage load 11 such as a motor. The inverter 14 has a function of converting a DC current from the high-voltage battery 12 into an AC current so as to rotate the motor (e.g., 3-phase AC motor).
The low-voltage circuit 20 includes a first switch portion 23 capable of connecting the low-voltage battery 22 to the low-voltage load 21.
The low-voltage battery 22 is composed of a plurality of secondary batteries 221 connected in series, and is capable of outputting a low voltage (e.g., 12 V) required for driving the low-voltage load 21 such as an illumination display portion 211 and acoustic equipment 212 (e.g., a radio or a stereo) as electronic equipment. The first switch portion 23 is an ignition switch and turns on/off the electric system of an entire vehicle. The first switch portion 23 is operated with the second switch portion 13. The ON operation of the first switch portion 23 turns on the second switch portion 13, and the OFF operation of the first switch portion 23 turns off the second switch portion 13, via a switch control portion 382′ of the leakage detection apparatus 300.
The leakage detection apparatus 300 includes a signal generator (fixed frequency) 310 for outputting a sine wave or square wave signal, an amplifier 32 for amplifying a signal from the signal generator 310 to a predetermined level, a resistor 33 for attenuating a signal from the amplifier 32 in accordance with an insulation resistor (not shown) between the high-voltage circuit 10 and the low-voltage circuit 20, a coupling capacitor for capacitance-coupling one end of the resistor 33 to the high-voltage circuit 10, a low-pass filter (LPF) 350 for removing a high-frequency component of a signal via the resistor 33 from the amplifier 32, an amplifier 36 for amplifying a signal from the LPF 350 to a predetermined level, an A/D converter 37 for sampling a signal from the amplifier 36 at a predetermined period and converting it into a digital signal, and a microcomputer (μCOM) 38 for receiving a digital signal from the A/D converter 37.
Furthermore, the μCOM 38 includes a leakage detection portion 381 for detecting the presence or absence of leakage by comparing a digital signal from the A/D converter 37 with a predetermined threshold value, and a switch control portion 382′ for receiving an ON operation signal of the first switch portion 23, and turning on the second switch portion 13 when a detection completion signal from the leakage detection portion 381 indicates the absence of leakage and keeping the second switch portion 13 in an OFF state when the detection completion signal from the leakage detection portion 381 indicates the presence of leakage.
The leakage detection portion 381 compares a digital signal from the A/D converter 37 with a predetermined threshold value, and detects the presence of leakage, when an insulation resistor between the high-voltage circuit 10 and the low-voltage circuit 20 becomes a predetermined value (e.g., 100 kΩ) or less and the digital signal decreases to a threshold value or less, and outputs the detection signal to the switch control portion 382′ and the illumination display portion 211 to light a leakage display lamp.
The switch control portion 382′ receives an ON operation signal of the first switch portion 23, and turns on the second switch portion 13 when the detection signal from the leakage detection portion 381 indicates the absence of leakage, and keeps the second switch portion 13 in an OFF state when the detection signal from the leakage detection portion 381 indicates the presence of leakage.
In the above-mentioned conventional leakage detection apparatus 300, the frequency of a signal output from the signal generator 310 is fixed at a low frequency (e.g., 1 Hz). The reason for this is as follows. In the signal from the signal generator 310, there is a switching noise of kHz order generated from the inverter 14 as noise to be superimposed via the coupling capacitor 34. In order to sufficiently attenuate this noise with an LPF 350, there is no choice but to set the signal generated by the signal generator 310 to be a low frequency (1 Hz).
Therefore, during startup, a period of time (confirmation time) required from a time when the ignition key switch is turned on to a time when the presence or absence of leakage is detected is prolonged.